I've used zmax and every other product on the market.
The main difference is with some they have to be re added or "boosted" every oil change.
I have blown up 2 motors on zmax.
Doesn't work at all.

Duralube is the only one that i have found where you add it and thats it for 50k miles but recently they watered down the formula.
I've run engines without oil pumps for weeks on duralube and have NEVER been able to blow up an engine while using the stuff.

Shark

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1984 W123 300CDT